Mauro Fabiano

Differential responses of bacteria, meiofauna and macrofauna in a shelf area (Ligurian Sea, NW Mediterranean): role of food availability

Abstract Density and biomass of bacteria, meio- and macrofauna were examined along a transect of eight stations (5–135 m depth) facing the estuary of the river Entella (Ligurian Sea) during summer 1990. Sediment samples were collected to determine organic detritus composition (total organic matter, lipid, protein and carbohydrate concentrations) and microphytobenthic biomass (as chlorophyll-a). Synoptic water samples were collected to determine the quantity and the quality of suspended matter (total suspended matter, particulate lipids, proteins, carbohydrates and chloroplastic pigments). Particulate organic matter in the surface water decreased from the coast towards the open sea both in quality and quantity. By contrast, the organic-matter concentration in the sediment increased with water depth. Quantity and biochemical composition of suspended and sedimentary organic matter affected the distribution of all the benthic assemblages. Bacteria appeared to be controlled by different parameters at different depths: generally they appeared to depend upon sediment particle surface and the quantity of organic matter, but when metazoan (particularly meiofauna) densities were high, grazing pressure might also exert a control on their abundance. The distribution of meio- and macrofauna along the continental shelf of the oligotrophic Ligurian Sea appears to depend more upon the quality of organic matter than on its quantity.

Deep-sea ecosystem response to climate changes: the eastern Mediterranean case study

Abstract Climate change is significantly modifying ecosystem functioning on a global scale, but little is known about the response of deep-sea ecosystems to such change. In the past decade, extensive climate change has modified the physico–chemical characteristics of deep waters in the eastern Mediterranean. Climate change has caused an immediate accumulation of organic matter on the deep-sea floor, altered the carbon and nitrogen cycles and has had negative effects on deep-sea bacteria and benthic fauna. Evidence from a miniature ocean model provides new ways of interpreting signals from the deep sea and indicates that, contrary to what might have been expected, deep-sea ecosystems do respond quickly to climate change.

Antibiotic resistance of benthic bacteria in fish-farm and control sediments of the Western Mediterranean

The effects of fish farming on bacterial density, biomass, community structure and their possible link to antibiotic resistance have been investigated in coastal sediments of the Ligurian Sea (Western Mediterranean). The top 2 cm of the sediment under a fish farm and control areas were analysed during summer 2000. Bacterial density and biomass were three folds higher (up to 3 x 10(10) cells/g and 2602.7 muC/g) (ANOVA, p < 0,0 1) in sediments beneath the fish cages compared to the control sediments. The number of Colony Forming Units (CFUs) for culturable bacteria and microbiological investigations indicated a shift in the relative importance of the Gram-negative bacteria in impacted sediments. Gram-positive bacteria increased their relevance in the control site where they represented up to 90% of total isolates. Antibiotic sensitivity tests showed a high percentage of resistant strains in both control and impacted sediments, which indicates a widespread antibiotic resistance within bacterial populations in areas surrounding fish farms. A high frequency of antibiotic resistance was observed for ampicillin (AMP) in impacted sediments (ANOVA, p < 0.05). Gram-negative bacteria displayed the highest resistance to ampicillin, and streptomycin (STR) (ANOVA, p < 0.05) and the shift in the structure of microbial assemblage was apparently related to the presence of Gram-negative resistant strains in fish-farm sediments. The incidence of multiple resistance patterns in bacterial isolates was also greater in impacted sediments and the presence of Bacillus strains producing antimicrobial compounds may be related to the high level of drug resistance. This study highlighted a major change occurring in the structure of the benthic bacterial community most probably due to fish farming and its close association with antibiotic resistance patterns

Enzymatically hydrolyzable protein and carbohydrate sedimentary pools as indicators of the trophic state of detritus sink systems: A case study in a Mediterranean coastal lagoon

In order to classify the trophic state of detritus sink systems, instead of the conventional indicators based on inorganic nutrient availability and algal biomass and productivity in the water column, we used new biochemical descriptors based on the amount of sedimentary organic carbon (C) and nitrogen (N) potentially available to heterotrophs. We investigated spatial and temporal changes in microphytobenthic biomass, organic matter biochemical composition, and enzymatically hydrolyzable protein and carbohydrate pools along a north-south transect in the Marsala lagoon (Mediterranean Sea, Italy) at three stations characterized by different hydrodynamic conditions and organic matter content in the sediment. In the Marsala lagoon water currents decreased from north to south and this pattern was reflected by organic matter distribution and composition. Sediment organic matter concentrations were among the highest reported in the literature and, in the central area where large meadows of the seagrassPosidonia oceanica were present, display a strong dominance of highly refractory carbohydrates. The protein to carbohydrate ratio was always < 1, indicating the dominance of aged organic detritus. Microphytobenthic biomass displayed an increasing pattern southward, and its contribution to the biopolymeric C pools ranged from negligible in the central sector of the lagoon to 50% in its northern part, indicating that sources of sediment organic C also changed along the hydrodynamic gradient. The percentage contribution of the enzymatically hydrolyzable fraction of proteins and carbohydrates was inversely related to total protein and total carbohydrate concentrations, respectively, suggesting that bioavailability of organic C and N increased with decreasing organic matter content in the sediment and with increasing hydrodynamic regime. Microphytobenthic contribution to biopolymeric C (as a proxy of autotrophic organic C) and the ratio of the enzymatically digestible fraction to biopolymeric C (as an indicator of organic matter liability) were significantly correlated, suggesting that chlorophylla sediment content might be used as an indicator of food promptly available to consumers. The present study also highlighted that the ratio of labile (i.e., enzymatically digestible) versus biopolymeric organic C in the sediments tends to decrease with increasing organic matter content, due to the increase of the refractory fraction of organic C.

Seasonal and spatial changes in the sediment organic matter of a semi-enclosed marine system (W-Mediterranean Sea)

The composition of sediment organic matter and the related role of microphytobenthic biomass have been investigated during one-year in a semi-enclosed marine system (Marsala lagoon, Mediterranean Sea). Monthly samples from June 1993 to May 1994 were analysed for carbohydrate, protein, lipid, photosynthetic pigment and total organic matter.The three main biochemical classes of organic compounds (i.e. carbohydrates, proteins and lipids) showed higher concentrations than reported in the literature. However, photosynthetic pigment was quite low, compared to other enclosed marine basins or Mediterranean coastal lagoons. As a result, the contribution of primary organic carbon to the sedimentary biopolymeric fraction of organic matter was low (on average 2.2%), indicating that most of the sedimentary organic matter in the study area originated from sources other than micro-algae. The sedimentary organic matter, dominated by carbohydrates (on average 51.2%) followed by proteins (39.0%) and lipids (9.8%), as well as the low protein to carbohydrate ratio, indicate the presence of large amounts of non-living and/or aged organic matter. Comparing data on spatial distribution of sedimentary and suspended organic matter, the dynamic balance of resuspension vs. sedimentation along a north-south axis is invoked as one major factor affecting the distribution and composition of the main classes of organic compounds. The macroalgal and vascular plant coverage is suggested to be another major factor affecting both amounts and composition of sedimentary organic matter. The northern area, characterised by partially unvegetated sediments, showed higher amounts of proteins, whilst moving southward and approaching a luxuriant Posidonia oceanica reef, carbohydrates became more important relative to proteins. As only the biopolymeric fraction of sediment organic matter showed significant seasonal changes, the quantity of sediment OM behaves as an emerging property. By contrast, OM quality is strictly connected to algal coverage as well as to episodic inputs of primary organic matter from deposited phytoplankton and/or microphytobenthos. The uncoupling between large amounts and relatively low nutritional value of sedimentary OM suggests that this particular environment behaves as a detrital ‘trap’.

Meiofauna of the deep Eastern Mediterranean Sea: distribution and abundance in relation to bacterial biomass, organic matter composition and other environmental factors

Abstract Quantitative information on the abundance and biomass of metazoan meiofauna was obtained from samples collected at 15 deep-sea stations in the Eastern Mediterranean Sea (533–2400m). Meiofaunal abundance was compared to bacterial biomass and other environmental factors such as the total sedimentary organic matter content, the concentrations of the main biochemical classes of organic compounds (i.e. proteins, carbohydrates and lipids) and to ATP. To estimate the sedimentation potential of primary organic matter, sediment bound chloroplastic pigment equivalents (CPE) were assayed. Meiofaunal density was very low ranging from 4 ind.10cm−2 (Station A4, 1658m depth) to 290 ind.10cm−2 (Station A12, 636m depth). Nematodes were the numerically dominant taxon (68% of total meiofauna) and were usually confined to the top 6cm of the sediments. Total meiofaunal biomass ranged from 2.78μgC 10cm−2 (Station A4) to 598.34μgC 10cm−2 (Station 15A). There was a significant decrease in the density of metazoan meiofauna with water depth. Bacterial biomass largely dominated the total biomass (as the sum of bacterial and meiofaunal biomass) with an average of 73.2% and accounted for 35.8% of the living biomass (as ATP carbon) whereas meiofaunal biomass accounted only for 6.56%. Bacterial biomass was significantly related to the DNA concentrations of the sediment. A significant correlation between ATP concentration and CPE content was also found. No correlations were found between meiofauna, ATP and CPE, or between meiofauna and bacterial parameters. The significant relationship between meiofaunal density and the ratio of labile organic matter/total organic matter indicates that deep-sea meiofauna inhabiting an extremely oligotrophic environment (such as the Eastern Mediterranean) may be more nutritionally dependent upon the quality than on the quantity of sedimentary organic matter.

Bacterial community structure and activity in fish farm sediments of the Ligurian sea (Western Mediterranean)

The environmental impact of a well-established fish farm has beeninvestigated in surface sediments of the Ligurian Sea in order to assess thebiodeposition, bacterial community structure and dynamics at a mature stage oforganic enrichment.The Biopolymeric carbon (BPC) fraction of organic matter and phytopigmentconcentrations displayed very high values beneath the fish cages. In particularlipid, carbohydrate and chlorophyll-a concentrations werehigher in farm sediment while protein concentrations did not show significantchange between farm sediment and control.Benthic bacteria were closely related to organic enrichment and their densitywas three times higher (up to 3 × 1010 cellsg−1) in stations beneath the cages being positivelycorrelated with BPC (n = 10, p < 0.05) and lipid (n = 10, p < 0.05)concentrations. Colony forming units (CFU) counts of heterotrophic bacteriaindicate a shift in the relative importance of the gram negative bacterialfraction, displaying the predominance of theCytophaga/Flexibacter-like bacteria (CBF), as well as theoccurrence of pathogenic bacteria (such as Vibrio) insediments beneath the farm. In contrast, Gram positive bacteria were moreprevalent in control site where they represented up to 90% of total isolates.Aminopeptidase activity displayed higher values in sediment beneath the cages,whereas the enzymatic activity per bacterial cell was lower. These data suggesta functional stress of bacterial degradation rates and represent a potentialvaluable environmental index of imbalance between supply and removal of organicmatter in eutrophicated environments.Data presented in this study also suggest that either the biochemicalcomposition of sedimentary organic matter as well as the selected microbialvariables may represent useful tools for evaluating the effects of organicenrichment due to fish farming and could be proposed as new environmentalindices of aquaculture impact on marine sediment.

Biochemical composition of sedimentary organic matter and bacterial distribution in the Aegean Sea: trophic state and pelagic–benthic coupling

Abstract Biochemical composition of sedimentary organic matter (OM), vertical fluxes and bacterial distribution were studied at 15 stations (95–2270 m depth) in the Aegean Sea during spring and summer. Downward fluxes of labile OM were significantly higher in the northern than in the southern part and were higher in summer than in spring. Primary inputs of OM were not related to sedimentary OM concentrations, which had highest values in summer. Sedimentary chlorophyll-a concentrations were similar in the northern and southern parts. Carbohydrates, the main component of sedimentary OM, were about 1.2 times higher in the southern part than in the northern, without significant temporal changes. Total proteins were higher in summer and about double in the northern part. Sedimentary proteins appeared more dependent upon the downward flux of phytopigment than of proteins. Sedimentary OM was characterised by a relatively large fraction of soluble compounds and showed better quality in the northern part. The lack of a depth-related pattern in sedimentary OM and the similar concentrations in the two areas suggest that differences in sedimentary OM quality in the Aegean basin are dependent on system productivity; the bulk of sedimentary OM is largely conservative. Sedimentary bacterial density was about double in the northern part and higher in spring than in summer, but bacterial size was about three times higher in summer, resulting in a larger bacterial biomass in summer. Bacterial density was coupled with total and protein fluxes, indicating a rapid bacterial response to pelagic production. Bacterial biomass was significantly correlated with sedimentary protein and phytopigment concentrations, indicating a clear response to accumulation of labile OM in the sediments. In all cases bacteria accounted for

Heterotrophic nanoflagellates, bacteria, and labile organic compounds in continental shelf and deep-sea sediments of the Eastern Mediterranean

A bstractThe abundance and biomass of heterotrophic nanoflagellates were examined in continental and deep-sea sediments of the Cretan Sea (Eastern Mediterranean); at depths of 40 to 1540 m. Nanoflagellate distribution was compared to the composition of sedimentary organic matter and bacterial standing stocks to investigate trophic interactions and factors potentially affecting distribution. Quantitative estimates were obtained using different samplers for testing whether the box corer is as effective as the multiplecorer for bacterial and protozoan population estimates. The sediments of the deep Cretan Sea appeared extremely deficient in organic nutrients, and were composed mostly (more than 90%) of detritus. Labile organic compounds (such as lipids, proteins, and soluble carbohydrates) were present at extremely low concentrations, decreasing with water depth. Refractory and structural carbohydrates were the dominant biochemical class. The decrease in food quality with depth was associated with a strong decline of the RNA:DNA ratio. Benthic bacteria were constrained by food availability, and reacted to different organic matter inputs (especially total carbohydrates) at different depths. Large size bacteria were significantly correlated with the amounts of proteins and chloroplastic pigments. Heterotrophic nanoflagellate distribution in the continental shelf and deep-sea sediments of the Cretan Sea was controlled by available food sources (i.e., labile organic compounds and bacteria). Flagellate density was significantly correlated with the concentration of food indicators (chlorophyll a, soluble carbohydrates, and lipids), and to bacterial number and biomass. Despite the oligotrophy of the system, flagellate densities were high (40–119 × 103 g−1) and dominated by small cells (3 to 6 μm in length). These results, coupled with the high nanoflagellate to bacterial biomass ratio (up to 0.27 at 40 m depth), suggest that benthic nanoflagellates may contribute significantly to the direct transfer of detrital carbon and bacterial biomass to the metazoan component of the food web in the Cretan Sea.

Organic matter composition in coastal sediments at Terra Nova Bay (Ross Sea) during summer 1995

Abstract We illustrate the spatial and vertical distribution of sediment phytopigments and organic matter biochemical composition at Terra Nova Bay (Ross Sea) during summer 1995. Coastal sediments displayed high phytopigments concentrations associated with huge amounts of labile organic matter largely dominated by proteins. This result was opposite to previous observations in the same area. Such comparison suggested that whilst organic matter quantity in the sediments depended upon the vertical input from the water column, temporal changes in its biochemical composition were related to benthic processes. As considerably high concentrations of biopolymeric organic carbon were found even at 6-cm depth and according to the “loss type” functioning of the coastal waters of the Ross Sea, we stress the summer time occurrence in coastal sediments of an important organic matter burial.